This invention relates in general to bearings and more particularly to bearing assemblies that are capable of monitoring angular velocity.
The automotive industry has turned to antilock brake systems to improve control over vehicles when the brakes of such vehicles are applied, particularly during emergency stops and braking on slippery surfaces. An antilock brake system must monitor the speed of each wheel to detect whenever a wheel locks up and begins to skid, so that the system may relax the braking effort applied to that wheel, at least to the point that the wheel again begins to rotate. With all wheels rotating, the driver maintains better control over the vehicle.
Typically, the hub for each road wheel carries a target or exciter wheel which rotates with the road wheel at the same angular velocity. As the target wheel turns, its periphery moves past a sensor which is generally fixed in position on the vehicle. The moving target wheel causes the sensor to generate a signal, which may be sinusoidal or simply pulses, but in any event is characterized by a frequency, and that signal along with corresponding signals from all of the other wheels are processed by a controller. Thus, the controller will sense when any one of the wheels locks up or rotates at a diminished velocity. On most automotive vehicles of current manufacture, the target wheels exist on the exterior surfaces of the wheel hubs where they are exposed to contaminants such as dirt and dust, as well as to corrosive chemicals. These substances may damage the target wheel or lodge in the air gap between it and the sensor and perhaps disrupt the sensor.
Some have suggested installing the target wheels within the hub, where they are isolated from foreign substances by the bearing seals, but these efforts have required substantial enlargement of the hubs to accommodate the target wheels.
The present invention resides in a bearing assembly which is quite compact, yet contains a target wheel and sensor that are isolated from exterior conditions by the seals which protect the rolling elements and raceways of the bearing. More specifically, the bearing assembly includes an outer race and two inner races, as well as rolling elements arranged in two rows between the outer race and the two inner races. The Seals close spaces between the ends of the outer race and the two inner races. The sensor fits into the outer race between the two rows of rolling elements. The target wheel fits over and interlocks with the ends of the two inner races .